38 WJEC Biology AS Level - Marianne Izen - 2nd Edition

Question 1

Answer 1

Question 2

Do animal cells contain vacuoles?

Answer 2

Yes, animal cells contain vacuoles

Question 3

Compare the vacuoles in animal cells to plant cells?

Answer 3

Unlike in plant cells, these are small, temporary vesicles and may occur in large numbers.

Question 4

Plasmodesma (plural = plasmodesmata) (Key Term)

Answer 4

Fine strands of cytoplasm that extend through pores in plant cell walls, connecting the cytoplasm of one cell with that of another.

Question 5

Which cells have centrioles?

Answer 5

Centrioles occur in all animal cells and most protoctistans but not in the cells of higher plants.

Question 6

Where are the centrioles located?

Answer 6

They are located just outside the nucleus.

Question 7

What is the structure of centrioles?

Answer 7

Centrioles are two rings of microtubules, making hollow cylinders positioned at right angles to one another.

Together, they are sometimes called the centrosome.

Question 8

What is the function of centrioles?

Answer 8

During cell division, centrioles organise the microtubules that make the spindle.

Question 9

Which cells have a vacuole?

Answer 9

Most plant cells have a large permanent vacuole

Question 10

What does a vacuole consist of?

Answer 10

Vacuole consists of a fluid-filled sac bounded by a single membrane, the tonoplast.

Question 11

What do vacuoles contain?

Answer 11

Vacuoles contain cell sap, a solution which stores chemicals such as glucose, amino acids and minerals, and may store vitamins and pigments, as in oranges.

Question 12

What is the function of vacuoles?

Answer 12

Vacuoles have a major role in supporting soft plant tissues.

Question 13

What is the cell wall of a plant cell made of?

Answer 13

The cell wall of a plant cell consists largely of cellulose.

Question 14

How is cellulose organised in the cell wall?

Answer 14

Cellulose molecules are held together in microfibrils, which are aggregated into fibres, embedded in a polysaccharide matrix called pectin.

Question 15

What are the functions of the cell wall?

Answer 15

The cell wall has the following functions:

1. Transport
2. Mechanical strength
3. Communication between cells

Question 16

How does the cell wall help in transport?

Answer 16

The gaps between the cellulose fibres make the cell wall fully permeable to water and dissolved molecules and ions.

This space outside the cells, through which solution moves, is called the apoplast.

The apoplast pathway is the main way that water crosses the plant root.

Question 17

How does the cell wall help in mechanical strength?

Answer 17

The structure of cellulose microfibrils and their laminated arrangement make the cell wall very strong.

When the vacuole is full of solution, the cell contents push against the cell wall, which resists expansion and the cell becomes turgid, supporting the plant.

Question 18

How does the cell wall help in communication between the cells?

Answer 18

Cell walls have pores, called pits, through which strands of cytoplasm, called plasmodesmata (singular - plasmodesma), pass.

The plasmodesma occurs where there is no cellulose thickening between two cells.

The strand of cytoplasm runs from one cell to the next.

The network of cytoplasm in connected cells is called the symplast.

The symplast pathway is important in water transport through a plant.

Question 19

What does this figure show?

Answer 19

Question 20

Draw the structure of a plasmodesma and name its parts

Answer 20